fix(socket): truncation when calling recv_slice

When calling `recv_slice`/`peek_slice` in the udp, icmp and raw
sockets, data is lost when the provided buffer is smaller than the
payload to be copied (not the case for `peek_slice` because it is not
dequeued).

With this commit, an `RecvError::Truncated` error is returned. In case
of UDP, the endpoint is also returned in the error. In case of ICMP, the
IP address is also returned in the error.

I implemented it the way Whitequark proposes it. Data is still lost, but
at least the caller knows that the data was truncated to the size of the
provided buffer. As Whitequark says, it is preferred to call `recv`
instead of `recv_slice` as there would be no truncation.

src/socket/icmp.rs

@@ -61,12 +61,14 @@ impl std::error::Error for SendError {}
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub enum RecvError {
     Exhausted,
+    Truncated,
 }
 
 impl core::fmt::Display for RecvError {
     fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         match self {
             RecvError::Exhausted => write!(f, "exhausted"),
+            RecvError::Truncated => write!(f, "truncated"),
         }
     }
 }
@@ -130,8 +132,8 @@ impl<'a> Socket<'a> {
     /// Create an ICMP socket with the given buffers.
     pub fn new(rx_buffer: PacketBuffer<'a>, tx_buffer: PacketBuffer<'a>) -> Socket<'a> {
         Socket {
-            rx_buffer: rx_buffer,
-            tx_buffer: tx_buffer,
+            rx_buffer,
+            tx_buffer,
             endpoint: Default::default(),
             hop_limit: None,
             #[cfg(feature = "async")]
@@ -394,9 +396,17 @@ impl<'a> Socket<'a> {
     /// Dequeue a packet received from a remote endpoint, copy the payload into the given slice,
     /// and return the amount of octets copied as well as the `IpAddress`
     ///
+    /// **Note**: when the size of the provided buffer is smaller than the size of the payload,
+    /// the packet is dropped and a `RecvError::Truncated` error is returned.
+    ///
     /// See also [recv](#method.recv).
     pub fn recv_slice(&mut self, data: &mut [u8]) -> Result<(usize, IpAddress), RecvError> {
         let (buffer, endpoint) = self.recv()?;
+
+        if data.len() < buffer.len() {
+            return Err(RecvError::Truncated);
+        }
+
         let length = cmp::min(data.len(), buffer.len());
         data[..length].copy_from_slice(&buffer[..length]);
         Ok((length, endpoint))
@@ -555,7 +565,7 @@ impl<'a> Socket<'a> {
                         dst_addr,
                         next_header: IpProtocol::Icmp,
                         payload_len: repr.buffer_len(),
-                        hop_limit: hop_limit,
+                        hop_limit,
                     });
                     emit(cx, (ip_repr, IcmpRepr::Ipv4(repr)))
                 }
@@ -592,7 +602,7 @@ impl<'a> Socket<'a> {
                         dst_addr,
                         next_header: IpProtocol::Icmpv6,
                         payload_len: repr.buffer_len(),
-                        hop_limit: hop_limit,
+                        hop_limit,
                     });
                     emit(cx, (ip_repr, IcmpRepr::Ipv6(repr)))
                 }
@@ -1096,6 +1106,42 @@ mod test_ipv6 {
         assert!(!socket.can_recv());
     }
 
+    #[rstest]
+    #[case::ethernet(Medium::Ethernet)]
+    #[cfg(feature = "medium-ethernet")]
+    fn test_truncated_recv_slice(#[case] medium: Medium) {
+        let (mut iface, _, _) = setup(medium);
+        let cx = iface.context();
+
+        let mut socket = socket(buffer(1), buffer(1));
+        assert_eq!(socket.bind(Endpoint::Ident(0x1234)), Ok(()));
+
+        let checksum = ChecksumCapabilities::default();
+
+        let mut bytes = [0xff; 24];
+        let mut packet = Icmpv6Packet::new_unchecked(&mut bytes[..]);
+        ECHOV6_REPR.emit(
+            &LOCAL_IPV6.into(),
+            &REMOTE_IPV6.into(),
+            &mut packet,
+            &checksum,
+        );
+
+        assert!(socket.accepts(cx, &REMOTE_IPV6_REPR, &ECHOV6_REPR.into()));
+        socket.process(cx, &REMOTE_IPV6_REPR, &ECHOV6_REPR.into());
+        assert!(socket.can_recv());
+
+        assert!(socket.accepts(cx, &REMOTE_IPV6_REPR, &ECHOV6_REPR.into()));
+        socket.process(cx, &REMOTE_IPV6_REPR, &ECHOV6_REPR.into());
+
+        let mut buffer = [0u8; 1];
+        assert_eq!(
+            socket.recv_slice(&mut buffer[..]),
+            Err(RecvError::Truncated)
+        );
+        assert!(!socket.can_recv());
+    }
+
     #[rstest]
     #[case::ethernet(Medium::Ethernet)]
     #[cfg(feature = "medium-ethernet")]

src/socket/raw.rs

@@ -57,12 +57,14 @@ impl std::error::Error for SendError {}
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub enum RecvError {
     Exhausted,
+    Truncated,
 }
 
 impl core::fmt::Display for RecvError {
     fn fmt(&self, f: &mut core::fmt::Formatter) -> core::fmt::Result {
         match self {
             RecvError::Exhausted => write!(f, "exhausted"),
+            RecvError::Truncated => write!(f, "truncated"),
         }
     }
 }
@@ -273,9 +275,16 @@ impl<'a> Socket<'a> {
 
     /// Dequeue a packet, and copy the payload into the given slice.
     ///
+    /// **Note**: when the size of the provided buffer is smaller than the size of the payload,
+    /// the packet is dropped and a `RecvError::Truncated` error is returned.
+    ///
     /// See also [recv](#method.recv).
     pub fn recv_slice(&mut self, data: &mut [u8]) -> Result<usize, RecvError> {
         let buffer = self.recv()?;
+        if data.len() < buffer.len() {
+            return Err(RecvError::Truncated);
+        }
+
         let length = min(data.len(), buffer.len());
         data[..length].copy_from_slice(&buffer[..length]);
         Ok(length)
@@ -303,9 +312,16 @@ impl<'a> Socket<'a> {
     /// and return the amount of octets copied without removing the packet from the receive buffer.
     /// This function otherwise behaves identically to [recv_slice](#method.recv_slice).
     ///
+    /// **Note**: when the size of the provided buffer is smaller than the size of the payload,
+    /// no data is copied into the provided buffer and a `RecvError::Truncated` error is returned.
+    ///
     /// See also [peek](#method.peek).
     pub fn peek_slice(&mut self, data: &mut [u8]) -> Result<usize, RecvError> {
         let buffer = self.peek()?;
+        if data.len() < buffer.len() {
+            return Err(RecvError::Truncated);
+        }
+
         let length = min(data.len(), buffer.len());
         data[..length].copy_from_slice(&buffer[..length]);
         Ok(length)
@@ -602,8 +618,7 @@ mod test {
                     socket.process(&mut cx, &$hdr, &$payload);
 
                     let mut slice = [0; 4];
-                    assert_eq!(socket.recv_slice(&mut slice[..]), Ok(4));
-                    assert_eq!(&slice, &$packet[..slice.len()]);
+                    assert_eq!(socket.recv_slice(&mut slice[..]), Err(RecvError::Truncated));
                 }
 
                 #[rstest]
@@ -641,10 +656,8 @@ mod test {
                     socket.process(&mut cx, &$hdr, &$payload);
 
                     let mut slice = [0; 4];
-                    assert_eq!(socket.peek_slice(&mut slice[..]), Ok(4));
-                    assert_eq!(&slice, &$packet[..slice.len()]);
-                    assert_eq!(socket.recv_slice(&mut slice[..]), Ok(4));
-                    assert_eq!(&slice, &$packet[..slice.len()]);
+                    assert_eq!(socket.peek_slice(&mut slice[..]), Err(RecvError::Truncated));
+                    assert_eq!(socket.recv_slice(&mut slice[..]), Err(RecvError::Truncated));
                     assert_eq!(socket.peek_slice(&mut slice[..]), Err(RecvError::Exhausted));
                 }
             }

src/socket/tcp.rs

@@ -1331,7 +1331,7 @@ impl<'a> Socket<'a> {
         // Rate-limit to 1 per second max.
         self.challenge_ack_timer = cx.now() + Duration::from_secs(1);
 
-        return Some(self.ack_reply(ip_repr, repr));
+        Some(self.ack_reply(ip_repr, repr))
     }
 
     pub(crate) fn accepts(&self, _cx: &mut Context, ip_repr: &IpRepr, repr: &TcpRepr) -> bool {

src/socket/udp.rs

@@ -88,12 +88,14 @@ impl std::error::Error for SendError {}
 #[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub enum RecvError {
     Exhausted,
+    Truncated,
 }
 
 impl core::fmt::Display for RecvError {
     fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {
             RecvError::Exhausted => write!(f, "exhausted"),
+            RecvError::Truncated => write!(f, "truncated"),
         }
     }
 }
@@ -393,9 +395,17 @@ impl<'a> Socket<'a> {
     /// Dequeue a packet received from a remote endpoint, copy the payload into the given slice,
     /// and return the amount of octets copied as well as the endpoint.
     ///
+    /// **Note**: when the size of the provided buffer is smaller than the size of the payload,
+    /// the packet is dropped and a `RecvError::Truncated` error is returned.
+    ///
     /// See also [recv](#method.recv).
     pub fn recv_slice(&mut self, data: &mut [u8]) -> Result<(usize, UdpMetadata), RecvError> {
         let (buffer, endpoint) = self.recv().map_err(|_| RecvError::Exhausted)?;
+
+        if data.len() < buffer.len() {
+            return Err(RecvError::Truncated);
+        }
+
         let length = min(data.len(), buffer.len());
         data[..length].copy_from_slice(&buffer[..length]);
         Ok((length, endpoint))
@@ -426,9 +436,17 @@ impl<'a> Socket<'a> {
     /// packet from the receive buffer.
     /// This function otherwise behaves identically to [recv_slice](#method.recv_slice).
     ///
+    /// **Note**: when the size of the provided buffer is smaller than the size of the payload,
+    /// no data is copied into the provided buffer and a `RecvError::Truncated` error is returned.
+    ///
     /// See also [peek](#method.peek).
     pub fn peek_slice(&mut self, data: &mut [u8]) -> Result<(usize, &UdpMetadata), RecvError> {
         let (buffer, endpoint) = self.peek()?;
+
+        if data.len() < buffer.len() {
+            return Err(RecvError::Truncated);
+        }
+
         let length = min(data.len(), buffer.len());
         data[..length].copy_from_slice(&buffer[..length]);
         Ok((length, endpoint))
@@ -851,11 +869,7 @@ mod test {
         );
 
         let mut slice = [0; 4];
-        assert_eq!(
-            socket.recv_slice(&mut slice[..]),
-            Ok((4, REMOTE_END.into()))
-        );
-        assert_eq!(&slice, b"abcd");
+        assert_eq!(socket.recv_slice(&mut slice[..]), Err(RecvError::Truncated));
     }
 
     #[rstest]
@@ -882,16 +896,8 @@ mod test {
         );
 
         let mut slice = [0; 4];
-        assert_eq!(
-            socket.peek_slice(&mut slice[..]),
-            Ok((4, &REMOTE_END.into()))
-        );
-        assert_eq!(&slice, b"abcd");
-        assert_eq!(
-            socket.recv_slice(&mut slice[..]),
-            Ok((4, REMOTE_END.into()))
-        );
-        assert_eq!(&slice, b"abcd");
+        assert_eq!(socket.peek_slice(&mut slice[..]), Err(RecvError::Truncated));
+        assert_eq!(socket.recv_slice(&mut slice[..]), Err(RecvError::Truncated));
         assert_eq!(socket.peek_slice(&mut slice[..]), Err(RecvError::Exhausted));
     }